Washington implemented tough unilateral sanctions against the Islamic Republic on Monday following President Trump's withdrawal from the Iran nuclear deal in May.

Russian Foreign Minister Sergei Lavrov has condemned Washington's decision to slap Tehran with sanctions, calling the restrictions "absolutely illegitimate" and deeply disappointing, and saying that it was "unacceptable" to hold dialogue in the language of ultimatums.

"As far as the US measures against Iran are concerned, they are absolutely illegitimate," Lavrov said on Tuesday in Madrid following a meeting with Spanish officials.